The present invention generally concerns the chilling of liquid and soft solid materials, such as foodstuffs, sludge, solutions and suspensions using a liquid cryogen such as liquid nitrogen as the cooling medium. In the processing of soft solid and liquid materials such as foodstuffs as, for example, meat, poultry, seafood, vegetable products, bakery products and the like, it is typically necessary to first chill the foodstuffs before commencing further processing (i.e. forming) operations. In order to chill foodstuffs it is common to employ blending devices in which the foodstuffs are mixed with the cooling medium to reduce the average temperature thereof to a desired level.
Cryogenic carbon dioxide and nitrogen have been used as a cooling medium for reducing the temperature of foodstuffs. For example, Scott T. Madsen et al., U.S. Pat. No. 4,476,686 discloses the supply of carbon dioxide gas and snow to a blender at a location below the surface of the foodstuffs. This process is stated to provide improvements over systems that supply carbon dioxide to the top of the blender. In particular, injection of carbon dioxide into the top of the blender results in inefficient blending of the carbon dioxide gas with the foodstuffs and a loss of a portion of the solid carbon dioxide due to sublimation before mixing.
It is also known in the art to inject liquid nitrogen into the top of a blender as described above for the injection of carbon dioxide.
Such methods adequately accomplish the task of chilling of the foodstuffs. However, there are disadvantages associated with such systems. For example, gaseous vapor present in the liquid cryogen feed and/or formed during the cooling process is typically vented to the atmosphere and its cooling capacity is thereby lost. In addition, the blenders typically employed for mixing the cryogen and the foodstuffs do not effectively disperse the liquid cryogen among the foodstuffs. Accordingly, prior art systems tend to result in the uneven chilling of the foodstuffs. Furthermore, prior art systems must be routinely shut down and cleaned to remove the buildup of food particles which adhere to the apparatus because of the presence of residual liquid cryogen.
There is therefore a continuing need to improve the efficiency of systems for the cooling of soft solid and liquid materials, such as foodstuffs within a blending device and a further need to effectively employ the cold vapor resulting from the cooling process rather than merely venting the same to the atmosphere.